Flavaglines target primitive leukemia cells and enhance anti-leukemia drug activity

RNA binding protein-directed control of leukemic stem cell evolution and function

Strict control over hematopoietic stem cell decision making is essential for healthy life-long blood production and underpins the origins of hematopoietic diseases. Acute myeloid leukemia (AML) in particular is a devastating hematopoietic malignancy that arises from the clonal evolution of disease-initiating primitive cells which acquire compounding genetic changes over time and culminate in the generation of leukemic stem cells (LSCs). Understanding the molecular underpinnings of these driver cells throughout their development will be instrumental in the interception of leukemia, the enabling of effective treatment of pre-leukemic conditions, as well as the development of strategies to target frank AML disease. To this point, a number of precancerous myeloid disorders and age-related alterations are proving as instructive models to gain insights into the initiation of LSCs. Here, we explore this myeloid dysregulation at the level of post-transcriptional control, where RNA-binding proteins (RBPs) function as core effectors. Through regulating the interplay of a myriad of RNA metabolic processes, RBPs orchestrate transcript fates to govern gene expression in health and disease. We describe the expanding appreciation of the role of RBPs and their post-transcriptional networks in sustaining healthy hematopoiesis and their dysregulation in the pathogenesis of clonal myeloid disorders and AML, with a particular emphasis on findings described in human stem cells. Lastly, we discuss key breakthroughs that highlight RBPs and post-transcriptional control as actionable targets for precision therapy of AML.

Silvestrol, a potent anticancer agent with unfavourable pharmacokinetics: Current knowledge on its pharmacological properties and future directions for the development of novel drugs

Cancer remains a leading cause of death, with increasing incidence. Conventional treatments offer limited efficacy and cause significant side effects, hence novel drugs with improved pharmacological properties and safety are required. Silvestrol (SLV) is a flavagline derived from some plants of the Aglaia genus that has shown potent anticancer effects, warranting further study. Despite its efficacy in inhibiting the growth of several types of cancer cells, SLV is characterized by an unfavorable pharmacokinetics that hamper its use as a drug. A consistent research over the recent years has led to develop novel SLV derivatives with comparable pharmacodynamics and an ameliorated pharmacokinetic profile, demonstrating potential applications in the clinical management of cancer. This comprehensive review aims to highlight the most recent data available on SLV and its synthetic derivatives, addressing their pharmacological profile and therapeutic potential in cancer treatment. A systematic literature review of both in vitro and in vivo studies focusing on anticancer effects, pharmacodynamics, and pharmacokinetics of these compounds is presented. Overall, literature data highlight that rationale chemical modifications of SLV are critical for the development of novel drugs with high efficacy on a broad variety of cancers and improved bioavailability in vivo. Nevertheless, SLV analogues need to be further studied to better understand their mechanisms of action, which can be partially different to SLV. Furthermore, clinical research is still required to assess their efficacy in humans and their safety.

Prohibitin 1 inhibits cell proliferation and induces apoptosis via the p53-mediated mitochondrial pathway in vitro

BACKGROUND

Prohibitin 1 (PHB1) has been identified as an antiproliferative protein that is highly conserved and ubiquitously expressed, and it participates in a variety of essential cellular functions, including apoptosis, cell cycle regulation, proliferation, and survival. Emerging evidence indicates that PHB1 may play an important role in the progression of hepatocellular carcinoma (HCC). However, the role of PHB1 in HCC is controversial.

AIM

To investigate the effects of PHB1 on the proliferation and apoptosis of human HCC cells and the relevant mechanisms in vitro.

METHODS

HCC patients and healthy individuals were enrolled in this study according to the inclusion and exclusion criteria; then, PHB1 levels in the sera and liver tissues of these participates were determined using ELISA, RT-PCR, and immunohistochemistry. Human HepG2 and SMMC-7721 cells were transfected with the pEGFP-PHB1 plasmid and PHB1-specific shRNA (shRNA-PHB1) for 24-72 h. Cell proliferation was analysed with an MTT assay. Cell cycle progression and apoptosis were analysed using flow cytometry (FACS). The mRNA and protein expression levels of the cell cycle-related molecules p21, Cyclin A2, Cyclin E1, and CDK2 and the cell apoptosis-related molecules cytochrome C (Cyt C), p53, Bcl-2, Bax, caspase 3, and caspase 9 were measured by real-time PCR and Western blot, respectively.

RESULTS

Decreased levels of PHB1 were found in the sera and liver tissues of HCC patients compared to those of healthy individuals, and decreased PHB1 was positively correlated with low differentiation, TNM stage III-IV, and alpha-fetoprotein ≥ 400 μg/L. Overexpression of PHB1 significantly inhibited human HCC cell proliferation in a time-dependent manner. FACS revealed that the overexpression of PHB1 arrested HCC cells in the G0/G1 phase of the cell cycle and induced apoptosis. The proportion of cells in the G0/G1 phase was significantly increased and the proportion of cells in the S phase was decreased in HepG2 cells that were transfected with pEGFP-PHB1 compared with untreated control and empty vector-transfected cells. The percentage of apoptotic HepG2 cells that were transfected with pEGFP-PHB1 was 15.41% ± 1.06%, which was significantly greater than that of apoptotic control cells (3.65% ± 0.85%, P < 0.01) and empty vector-transfected cells (4.21% ± 0.52%, P < 0.01). Similar results were obtained with SMMC-7721 cells. Furthermore, the mRNA and protein expression levels of p53, p21, Bax, caspase 3, and caspase 9 were increased while the mRNA and protein expression levels of Cyclin A2, Cyclin E1, CDK2, and Bcl-2 were decreased when PHB1 was overexpressed in human HCC cells. However, when PHB1 was upregulated in human HCC cells, Cyt C expression levels were increased in the cytosol and decreased in the mitochondria, which indicated that Cyt C had been released into the cytosol. Conversely, these effects were reversed when PHB1 was knocked down.

CONCLUSION

PHB1 inhibits human HCC cell viability by arresting the cell cycle and inducing cell apoptosis via activation of the p53-mediated mitochondrial pathway.

Phytochemicals and bioactive compounds effective against acute myeloid leukemia: A systematic review

This systematic review identified various bioactive compounds which have the potential to serve as novel drugs or leads against acute myeloid leukemia. Acute myeloid leukemia (AML) is a heterogeneous hematopoietic malignancy that arises from the dysregulation of cell differentiation, proliferation, and cell death. The risk factors associated with the onset of AML include long-term exposure to radiation and chemicals such as benzene, smoking, genetic disorders, blood disorders, advancement in age, and others. Although novel strategies to manage AML, including a refinement of the conventional chemotherapy regimens, hypomethylating agents, and molecular targeted drugs, have been developed in recent years, resistance and relapse remain the main clinical problems. In this study, three databases, PubMed/MEDLINE, ScienceDirect, and Google Scholar, were systematically searched to identify various bioactive compounds with antileukemic properties. A total of 518 articles were identified, out of which 59 were viewed as eligible for the current report. From the data extracted, over 60 bioactive compounds were identified and divided into five major groups: flavonoids, alkaloids, organosulfur compounds, terpenes, and terpenoids, and other known and emerging bioactive compounds. The mechanism of actions of the analyzed individual bioactive molecules differs remarkably and includes disrupting chromatin structure, upregulating the synthesis of certain DNA repair proteins, inducing cell cycle arrest and apoptosis, and inhibiting/regulating Hsp90 activities, DNA methyltransferase 1, and histone deacetylase 1.

RNA-binding proteins in cancer drug discovery

RNA-binding proteins (RBPs) are crucial players in tumorigenesis and, hence, promising targets in cancer drug discovery. However, they are largely regarded as 'undruggable', because of the often noncatalytic and complex interactions between protein and RNA, which limit the discovery of specific inhibitors. Nonetheless, over the past 10 years, drug discovery efforts have uncovered RBP inhibitors with clinical relevance, highlighting the disruption of RNA-protein networks as a promising avenue for cancer therapeutics. In this review, we discuss the role of structurally distinct RBPs in cancer, and the mechanisms of RBP-directed small-molecule inhibitors (SMOIs) focusing on drug-protein interactions, binding surfaces, potency, and translational potential. Additionally, we underline the limitations of RBP-targeting drug discovery assays and comment on future trends in the field.

Reanalysis of ribosome profiling datasets reveals a function of rocaglamide A in perturbing the dynamics of translation elongation via eIF4A

The quickly accumulating ribosome profiling data is an insightful resource for studying the critical details of translation regulation under various biological contexts. Rocaglamide A (RocA), an antitumor heterotricyclic natural compound, has been shown to inhibit translation initiation of a large group of mRNA species by clamping eIF4A onto poly-purine motifs in the 5' UTRs. However, reanalysis of previous ribosome profiling datasets reveals an unexpected shift of the ribosome occupancy pattern, upon RocA treatment in various types of cells, during early translation elongation for a specific group of mRNA transcripts without poly-purine motifs over-represented in their 5' UTRs. Such perturbation of translation elongation dynamics can be attributed to the blockage of translating ribosomes due to the binding of eIF4A to the poly-purine sequence in coding regions. In summary, our study presents the complete dual modes of RocA in blocking translation initiation and elongation, which underlie the potent antitumor effect of RocA.

EIF4A inhibition targets bioenergetic homeostasis in AML MOLM-14 cells in vitro and in vivo and synergizes with cytarabine and venetoclax

BACKGROUND

Acute myeloid leukemia (AML) is an aggressive hematological cancer resulting from uncontrolled proliferation of differentiation-blocked myeloid cells. Seventy percent of AML patients are currently not cured with available treatments, highlighting the need of novel therapeutic strategies. A promising target in AML is the mammalian target of rapamycin complex 1 (mTORC1). Clinical inhibition of mTORC1 is limited by its reactivation through compensatory and regulatory feedback loops. Here, we explored a strategy to curtail these drawbacks through inhibition of an important effector of the mTORC1signaling pathway, the eukaryotic initiation factor 4A (eIF4A).

METHODS

We tested the anti-leukemic effect of a potent and specific eIF4A inhibitor (eIF4Ai), CR-1-31-B, in combination with cytosine arabinoside (araC) or the BCL2 inhibitor venetoclax. We utilized the MOLM-14 human AML cell line to model chemoresistant disease both in vitro and in vivo. In eIF4Ai-treated cells, we assessed for changes in survival, apoptotic priming, de novo protein synthesis, targeted intracellular metabolite content, bioenergetic profile, mitochondrial reactive oxygen species (mtROS) and mitochondrial membrane potential (MMP).

RESULTS

eIF4Ai exhibits anti-leukemia activity in vivo while sparing non-malignant myeloid cells. In vitro, eIF4Ai synergizes with two therapeutic agents in AML, araC and venetoclax. EIF4Ai reduces mitochondrial membrane potential (MMP) and the rate of ATP synthesis from mitochondrial respiration and glycolysis. Furthermore, eIF4i enhanced apoptotic priming while reducing the expression levels of the antiapoptotic factors BCL2, BCL-XL and MCL1. Concomitantly, eIF4Ai decreases intracellular levels of specific metabolic intermediates of the tricarboxylic acid cycle (TCA cycle) and glucose metabolism, while enhancing mtROS. In vitro redox stress contributes to eIF4Ai cytotoxicity, as treatment with a ROS scavenger partially rescued the viability of eIF4A inhibition.

CONCLUSIONS

We discovered that chemoresistant MOLM-14 cells rely on eIF4A-dependent cap translation for survival in vitro and in vivo. EIF4A drives an intrinsic metabolic program sustaining bioenergetic and redox homeostasis and regulates the expression of anti-apoptotic proteins. Overall, our work suggests that eIF4A-dependent cap translation contributes to adaptive processes involved in resistance to relevant therapeutic agents in AML.

PLAG1 dampens protein synthesis to promote human hematopoietic stem cell self-renewal

Hematopoietic stem cell (HSC) dormancy is understood as supportive of HSC function and its long-term integrity. Although regulation of stress responses incurred as a result of HSC activation is recognized as important in maintaining stem cell function, little is understood of the preventive machinery present in human HSCs that may serve to resist their activation and promote HSC self-renewal. We demonstrate that the transcription factor PLAG1 is essential for long-term HSC function and, when overexpressed, endows a 15.6-fold enhancement in the frequency of functional HSCs in stimulatory conditions. Genome-wide measures of chromatin occupancy and PLAG1-directed gene expression changes combined with functional measures reveal that PLAG1 dampens protein synthesis, restrains cell growth and division, and enhances survival, with the primitive cell advantages it imparts being attenuated by addition of the potent translation activator, c-MYC. We find PLAG1 capitalizes on multiple regulatory factors to ensure protective diminished protein synthesis including 4EBP1 and translation-targeting miR-127 and does so independently of stress response signaling. Overall, our study identifies PLAG1 as an enforcer of human HSC dormancy and self-renewal through its highly context-specific regulation of protein biosynthesis and classifies PLAG1 among a rare set of bona fide regulators of messenger RNA translation in these cells. Our findings showcase the importance of regulated translation control underlying human HSC physiology, its dysregulation under activating demands, and the potential if its targeting for therapeutic benefit.

The Flavagline Compound 1-(2-(dimethylamino)acetyl)-Rocaglaol Induces Apoptosis in K562 Cells by Regulating the PI3K/Akt/mTOR, JAK2/STAT3, and MAPK Pathways

Purpose

Methods

Results

Conclusion

The splicing factor RBM17 drives leukemic stem cell maintenance by evading nonsense-mediated decay of pro-leukemic factors

Chemo-resistance in acute myeloid leukemia (AML) patients is driven by leukemic stem cells (LSCs) resulting in high rates of relapse and low overall survival. Here, we demonstrate that upregulation of the splicing factor, RBM17 preferentially marks and sustains LSCs and directly correlates with shorten patient survival. RBM17 knockdown in primary AML cells leads to myeloid differentiation and impaired colony formation and in vivo engraftment. Integrative multi-omics analyses show that RBM17 repression leads to inclusion of poison exons and production of nonsense-mediated decay (NMD)-sensitive transcripts for pro-leukemic factors and the translation initiation factor, EIF4A2. We show that EIF4A2 is enriched in LSCs and its inhibition impairs primary AML progenitor activity. Proteomic analysis of EIF4A2-depleted AML cells shows recapitulation of the RBM17 knockdown biological effects, including pronounced suppression of proteins involved in ribosome biogenesis. Overall, these results provide a rationale to target RBM17 and/or its downstream NMD-sensitive splicing substrates for AML treatment.

Comparative phytochemistry of flavaglines (= rocaglamides), a group of highly bioactive flavolignans from Aglaia species (Meliaceae)

Flavaglines are formed by cycloaddition of a flavonoid nucleus with a cinnamic acid moiety representing a typical chemical character of the genus Aglaia of the family Meliaceae. Based on biosynthetic considerations 148 derivatives are grouped together into three skeletal types representing 77 cyclopenta[b]benzofurans, 61 cyclopenta[bc]benzopyrans, and 10 benzo[b]oxepines. Apart from different hydroxy, methoxy, and methylenedioxy groups of the aromatic rings, important structural variation is created by different substitutions and stereochemistries of the central cyclopentane ring. Putrescine-derived bisamides constitute important building blocks occurring as cyclic 2-aminopyrrolidines or in an open-chained form, and are involved in the formation of pyrimidinone flavaglines. Regarding the central role of cinnamic acid in the formation of the basic skeleton, rocagloic acid represents a biosynthetic precursor from which aglafoline- and rocaglamide-type cyclopentabenzofurans can be derived, while those of the rocaglaol-type are the result of decarboxylation. Broad-based comparison revealed characteristic substitution trends which contribute as chemical markers to natural delimitation and grouping of taxonomically problematic Aglaia species. A wide variety of biological activities ranges from insecticidal, antifungal, antiprotozoal, and anti-inflammatory properties, especially to pronounced anticancer and antiviral activities. The high insecticidal activity of flavaglines is comparable with that of the well-known natural insecticide azadirachtin. Comparative feeding experiments informed about structure-activity relationships and exhibited different substitutions of the cyclopentane ring essential for insecticidal activity. Parallel studies on the antiproliferative activity of flavaglines in various tumor cell lines revealed similar structural prerequisites that let expect corresponding molecular mechanisms. An important structural modification with very high cytotoxic potency was found in the benzofuran silvestrol characterized by an unusual dioxanyloxy subunit. It possessed comparable cytotoxicity to that of the natural anticancer compounds paclitaxel (Taxol®) and camptothecin without effecting normal cells. The primary effect was the inhibition of protein synthesis by binding to the translation initiation factor eIF4A, an ATP-dependent DEAD-box RNA helicase. Flavaglines were also shown to bind to prohibitins (PHB) responsible for regulation of important signaling pathways, and to inhibit the transcriptional factor HSF1 deeply involved in metabolic programming, survival, and proliferation of cancer cells. Flavaglines were shown to be not only promising anticancer agents but gained now also high expectations as agents against emerging RNA viruses like SARS-CoV-2. Targeting the helicase eIF4A with flavaglines was recently described as pan-viral strategy for minimizing the impact of future RNA virus pandemics.

Update on Phytochemical and Biological Studies on Rocaglate Derivatives from Aglaia Species

With about 120 species, Aglaia is one of the largest genera of the plant family Meliaceae (the mahogany plants). It is native to the tropical rainforests of the Indo-Australian region, ranging from India and Sri Lanka eastward to Polynesia and Micronesia. Various Aglaia species have been investigated since the 1960s for their phytochemical constituents and biological properties, with the cyclopenta[b]benzofurans (rocaglates or flavaglines) being of particular interest. Phytochemists, medicinal chemists, and biologists have conducted extensive research in establishing these secondary metabolites as potential lead compounds with antineoplastic and antiviral effects, among others. The varied biological properties of rocaglates can be attributed to their unusual structures and their ability to act as inhibitors of the eukaryotic translation initiation factor 4A (eIF4A), affecting protein translation. The present review provides an update on the recently reported phytochemical constituents of Aglaia species, focusing on rocaglate derivatives. Furthermore, laboratory work performed on investigating the biological activities of these chemical constituents is also covered.

Natural Products as a Promising Therapeutic Strategy to Target Cancer Stem Cells

Cancer is still a deadly disease, and its treatment desperately needs to be managed in a very sophisticated way through fast-developing novel strategies. Most of the cancer cases eventually develop into recurrencies, for which cancer stem cells (CSCs) are thought to be responsible. They are considered as a subpopulation of all cancer cells of tumor tissue with aberrant regulation of self-renewal, unbalanced proliferation, and cell death properties. Moreover, CSCs show a serious degree of resistance to chemotherapy or radiotherapy and immune surveillance as well. Therefore, new classes of drugs are rushing into the market each year, which makes the cost of therapy increase dramatically. Natural products are also becoming a new research area as a diverse chemical library to suppress CSCs. Some of the products even show promise in this regard. So, the near future could witness the introduction of natural products as a source of new chemotherapy modalities, which may result in the development of novel anticancer drugs. They could also be a reasonably-priced alternative to highly expensive current treatments. Nowadays, considering the effects of natural compounds on targeting surface markers, signaling pathways, apoptosis, and escape from immunosurveillance have been a highly intriguing area in preclinical and clinical research. In this review, we present scientific advances regarding their potential use in the inhibition of CSCs and the mechanisms by which they kill the CSCs.

Natural products as drugs and tools for influencing core processes of eukaryotic mRNA translation

Eukaryotic protein synthesis is the highly conserved, complex mechanism of translating genetic information into proteins. Although this process is essential for cellular homoeostasis, dysregulations are associated with cellular malfunctions and diseases including cancer and diabetes. In the challenging and ongoing search for adequate treatment possibilities, natural products represent excellent research tools and drug leads for new interactions with the translational machinery and for influencing mRNA translation. In this review, bacterial-, marine- and plant-derived natural compounds that interact with different steps of mRNA translation, comprising ribosomal assembly, translation initiation and elongation, are highlighted. Thereby, the exact binding and interacting partners are unveiled in order to accurately understand the mode of action of each natural product. The pharmacological relevance of these compounds is furthermore assessed by evaluating the observed biological activities in the light of translational inhibition and by enlightening potential obstacles and undesired side-effects, e.g. in clinical trials. As many of the natural products presented here possess the potential to serve as drug leads for synthetic derivatives, structural motifs, which are indispensable for both mode of action and biological activities, are discussed. Evaluating the natural products emphasises the strong diversity of their points of attack. Especially the fact that selected binding partners can be set in direct relation to different diseases emphasises the indispensability of natural products in the field of drug development. Discovery of new, unique and unusual interacting partners again renders them promising tools for future research in the field of eukaryotic mRNA translation.

Cytotoxic and Apoptotic Activity of Aglaforbesin Derivative Isolated from Aglaia loheri Merr. on HCT116 Human Colorectal Cancer Cells

Background:

The genus Aglaia (Meliaceae) is an established source of many anticancer compounds. The study evaluated the leaf extracts of Aglaia loheri, a tree native to the Philippines, as potential source of anticancer compounds.

Methods:

Using bioassay-guided fractionation, A. loheri leaf extract was subjected to various chromatographic techniques and step-wise application of MTT assay on human colorectal carcinoma cells, HCT116, to determine the cytotoxic fractions. The most cytotoxic HPLC isolate was structurally identified using 1D and 2D NMR and its apoptotic effect was assessed by JC-1 staining, caspase 3/7 assay and TUNEL assay.

Results:

After stepwise chromatography fractionation, an HPLC isolate, structurally identified as aglaforbesin derivative (AFD), demonstrated potent cytotoxicity against HCT116. AFD exhibited strong toxicity (IC₅₀ = 1.13 ±0.07 µg/mL) and high selectivity on HCT116 than normal human kidney cells (HK-2). AFD-induced toxicity to HCT116 is possibly through the stimulation of the apoptotic signaling pathway via caspase 3/7 activation and DNA fragmentation independent of mitochondrial membrane depolarization.

Conclusion:

AFD exhibited selective cytotoxicity and apoptotic activity to HCT116 and could be further developed as anticancer drug lead.

Targeting acute myeloid leukemia stem cells: Current therapies in development and potential strategies with new dimensions

High relapse rate of acute myeloid leukemia (AML) is still a crucial problem despite considerable advances in anti-cancer therapies. One crucial cause of relapse is the existence of leukemia stem cells (LSCs) with self-renewal ability, which contribute to repeated treatment resistance and recurrence. Treatments targeting LSCs, especially in combination with existing chemotherapy regimens or hematopoietic stem cell transplantation might help achieve a higher complete remission rate and improve overall survival. Many novel agents of different therapeutic strategies that aim to modulate LSCs self-renewal, proliferation, apoptosis, and differentiation are under investigation. In this review, we summarize the latest advances of different therapies in development based on the biological characteristics of LSCs, with particular attention on natural products, synthetic compounds, antibody therapies, and adoptive cell therapies that promote the LSC eradication. We also explore the causes of AML recurrence and proposed potential strategies with new dimensions for targeting LSCs in the future.

Targeting Protein Translation by Rocaglamide and Didesmethylrocaglamide to Treat MPNST and Other Sarcomas

Malignant peripheral nerve sheath tumors (MPNST) frequently overexpress eukaryotic initiation factor 4F components, and the eIF4A inhibitor silvestrol potently suppresses MPNST growth. However, silvestrol has suboptimal drug-like properties, including a bulky structure, poor oral bioavailability (<2%), sensitivity to MDR1 efflux, and pulmonary toxicity in dogs. We compared ten silvestrol-related rocaglates lacking the dioxanyl ring and found that didesmethylrocaglamide (DDR) and rocaglamide (Roc) had growth-inhibitory activity comparable with silvestrol. Structure-activity relationship analysis revealed that the dioxanyl ring present in silvestrol was dispensable for, but may enhance, cytotoxicity. Both DDR and Roc arrested MPNST cells at G2-M, increased the sub-G1 population, induced cleavage of caspases and PARP, and elevated the levels of the DNA-damage response marker γH2A.X, while decreasing the expression of AKT and ERK1/2, consistent with translation inhibition. Unlike silvestrol, DDR and Roc were not sensitive to MDR1 inhibition. Pharmacokinetic analysis confirmed that Roc had 50% oral bioavailability. Importantly, Roc, when administered intraperitoneally or orally, showed potent antitumor effects in an orthotopic MPNST mouse model and did not induce pulmonary toxicity in dogs as found with silvestrol. Treated tumors displayed degenerative changes and had more cleaved caspase-3-positive cells, indicative of increased apoptosis. Furthermore, Roc effectively suppressed the growth of osteosarcoma, Ewing sarcoma, and rhabdomyosarcoma cells and patient-derived xenografts. Both Roc- and DDR-treated sarcoma cells showed decreased levels of multiple oncogenic kinases, including insulin-like growth factor-1 receptor. The more favorable drug-like properties of DDR and Roc and the potent antitumor activity of Roc suggest that these rocaglamides could become viable treatments for MPNST and other sarcomas.

Flavagline analog FL3 induces cell cycle arrest in urothelial carcinoma cell of the bladder by inhibiting the Akt/PHB interaction to activate the GADD45α pathway

BACKGROUND

Prohibitin 1 (PHB) is a potential target for the treatment of urothelial carcinoma of the bladder (UCB). FL3 is a newly synthesized agent that inhibits cancer cell proliferation by targeting the PHB protein; however, the effect of FL3 in UCB cells remains unexplored.

METHODS

FL3 was identified to be a potent inhibitor of UCB cell viability using CCK-8 (cell counting kit-8) assay. Then a series of in vitro and in vivo experiments were conducted to further demonstrate the inhibitory effect of FL3 on UCB cell proliferation and to determine the underlying mechanisms.

RESULTS

FL3 inhibited UCB cell proliferation and growth both in vitro and in vivo. By targeting the PHB protein, FL3 inhibited the interaction of Akt and PHB as well as Akt-mediated PHB phosphorylation, which consequently decreases the localization of PHB in the mitochondria. In addition, FL3 treatment resulted in cell cycle arrest in the G2/M phase, and this inhibitory effect of FL3 could be mimicked by knockdown of PHB. Through the microarray analysis of mRNA expression after FL3 treatment and knockdown of PHB, we found that the mRNA expression of the growth arrest and DNA damage-inducible alpha (GADD45α) gene were significantly upregulated. When knocked down the expression of GADD45α, the inhibitory effect of FL3 on cell cycle was rescued, suggesting that FL3-induced cell cycle inhibition is GADD45α dependent.

CONCLUSION

Our data provide that FL3 inhibits the interaction of Akt and PHB, which in turn activates the GADD45α-dependent cell cycle inhibition in the G2/M phase.

Anticancer Natural Compounds as Epigenetic Modulators of Gene Expression

Accumulating evidence shows that hallmarks of cancer include: "genetic and epigenetic alterations leading to inactivation of cancer suppressors, overexpression of oncogenes, deregulation of intracellular signaling cascades, alterations of cancer cell metabolism, failure to undergo cancer cell death, induction of epithelial to mesenchymal transition, invasiveness, metastasis, deregulation of immune response and changes in cancer microenvironment, which underpin cancer development". Natural compounds as bioactive ingredients isolated from natural sources (plants, fungi, marine life forms) have revolutionized the field of anticancer therapeutics and rapid developments in preclinical studies are encouraging. Natural compounds could affect the epigenetic molecular mechanisms that modulate gene expression, as well as DNA damage and repair mechanisms. The current review will describe the latest achievements in using naturally produced compounds targeting epigenetic regulators and modulators of gene transcription in vitro and in vivo to generate novel anticancer therapeutics.

Assessment of flavaglines as potential chikungunya virus entry inhibitors

Chikungunya virus (CHIKV) is a re‐emerging mosquito‐borne alphavirus that recently caused large epidemics in islands in, and countries around, the Indian Ocean. There is currently no specific drug for therapeutic treatment or for use as a prophylactic agent against infection and no commercially available vaccine. Prohibitin has been identified as a receptor protein used by chikungunya virus to enter mammalian cells. Recently, synthetic sulfonyl amidines and flavaglines (FLs), a class of naturally occurring plant compounds with potent anti‐cancer and cytoprotective and neuroprotective activities, have been shown to interact directly with prohibitin. This study therefore sought to determine whether three prohibitin ligands (sulfonyl amidine 1 m and the flavaglines FL3 and FL23) were able to inhibit CHIKV infection of mammalian Hek293T/17 cells. All three compounds inhibited infection and reduced virus production when cells were treated before infection but not when added after infection. Pretreatment of cells for only 15 minutes prior to infection followed by washing out of the compound resulted in significant inhibition of entry and virus production. These results suggest that further investigation of prohibitin ligands as potential Chikungunya virus entry inhibitors is warranted.

Unveiling the potential of prohibitin in cancer

Recently, research has shed new light on the role of Prohibitin (PHB) in cancer pathogenesis across an array of cancer types. Important mechanisms for PHB have been unveiled in several cancers, especially with regard to the androgen independent state of prostate cancer (PC) and oestrogen dependent breast cancer. However, PHB is often overlooked due to its complex but subtle roles within the cell. Having gathered both historical and current research exploring PHB's role in different cancer types including prostate and breast, here we aim to pair this information with its molecular properties in the hope of translating this information into a clinical perspective, thus discussing its possible use in future cancer therapy.

Biomimetic kinetic resolution: highly enantio- and diastereoselective transfer hydrogenation of aglain ketones to access flavagline natural products

We have previously reported asymmetric syntheses and absolute configuration assignments of the aglains (+)-ponapensin and (+)-elliptifoline and proposed a biosynthetic kinetic resolution process to produce enantiomeric rocaglamides and aglains. Herein, we report a biomimetic approach for the synthesis of enantiomerically enriched aglains and rocaglamides via kinetic resolution of a bridged ketone utilizing enantioselective transfer hydrogenation. The methodology has been employed to synthesize and confirm the absolute stereochemistries of the pyrimidone rocaglamides (+)-aglaiastatin and (-)-aglaroxin C. Additionally, the enantiomers and racemate of each metabolite were assayed for inhibition of the heat-shock response, cytotoxicity, and translation inhibition.

Molecular mechanisms and anti-cancer aspects of the medicinal phytochemicals rocaglamides (=flavaglines)

Rocaglamides (= flavaglines) are potent natural anti-cancer phytochemicals that inhibit cancer growth at nanomolar concentrations by the following mechanisms: (1) inhibition of translation initiation via inhibition of phosphorylation of the mRNA cap-binding eukaryotic translation initiation factor eIF4E and stabilization of RNA-binding of the translation initiation factor eIF4A in the eIF4F complex; (2) blocking cell cycle progression by activation of the ATM/ATR-Chk1/Chk2 checkpoint pathway; (3) inactivation of the heat shock factor 1 (HSF1) leading to up-regulation of thioredoxin-interacting protein (TXNIP) and consequent reduction of glucose uptake and (4) induction of apoptosis through activation of the MAPK p38 and JNK and inhibition of the Ras-CRaf-MEK-ERK signaling pathway. Besides the anti-cancer activities, rocaglamides are also shown to protect primary cells from chemotherapy-induced cell death and alleviate inflammation- and drug-induced injury in neuronal tissues. This review will focus on the recently discovered molecular mechanisms of the actions of rocaglamides and highlights the benefits of using rocaglamides in cancer treatment.